1. Field of the Invention
The present invention relates to novel thiadiazinone derivatives or salts thereof which are useful as a cardiotonic drug.
2. Discussion of the Background
Cardiotonic drugs directly act on the heart and promote its contraction. Various kinds of the drugs have been conventionally utilized for the treatment of heart failure.
Examples of the drugs which are known to have a cardiotonic activity and have been conventionally utilized are as follows: pyridazinone derivatives (Japanese Laid-Open Patent Publication Nos. 8015/83, 8016/83, 87283/85, 183282/86, 154670/88, 148865/83, 183618/83, 203978/83 and 84883/84, U.S. Pat. Nos. 4661484and 4971968, European Laid-Open Patent Publication No. 85985, and the like); pyridazine-3-thione derivatives (Japanese Patent Nos. 188815/83 and 203977/83, and the like); pyridine derivatives (Japanese Laid-Open Patent Publication No. 197681/85, and the like); pyridone derivatives (Japanese Laid-Open Patent Publication No.59571/90and the like); 2(1H)-pyrimidinone derivatives (Japanese Laid-Open Patent Publication No.59573/90, and the like); pyradinone derivatives (Japanese Laid-Open Patent Publication No. 59574/90); and thiazolone derivatives (Japanese Patent No. 59577/90, and the like).
However, the conventionally-used cardiotonic drugs as stated above have the following disadvantages: they have very narrow safety margins; they can cause arrhythmia; their cardiotonic action is transient; and they are not suitable for oral administration.